1. Field of the Invention
The present invention relates to a display apparatus in which organic electroluminescent (EL) elements, each of which uses a silver thin film as an electrode at a light extraction side, are arranged.
2. Description of the Related Art
An organic EL element has the structure in which an organic compound layer including a luminous layer is provided between an anode and a cathode, and at least one electrode at a light extraction side (hereinafter referred to as a “light extraction-side electrode” in some cases) is required to be transparent. As the transparent electrode, for example, an oxide transparent electrode formed, for example, of indium tin oxide (ITO) is generally used.
In addition, an attempt to use a metal thin film as the transparent electrode has been carried out in order to obtain higher transmittance and electrical conductivity. As a material for the metal thin film, for example, gold, silver, or copper, each of which has high electrical conductivity and transmittance in the visible light region, may be mentioned. Among these mentioned above, since the wavelength dependence of the transmittance is flat and the electrical conductivity is also high, silver is promising. However, even if silver is formed into a thin film, its transmittance is not simply improved. One of the reasons for this is a localized surface plasmon absorption of silver (see J. J. Mock, D. R. Smith, S. Schultz, “Local Refractive Index Dependence of Plasmon Resonance Spectra from Individual Nanoparticles”, Nano Letters, 2003, Vol. 3, No. 4, pp. 485-491).
In general, when the thickness of a silver thin film is decreased to approximately 10 nm in order to improve the transmittance, this thin film is placed into a discontinuous island state instead of forming a continuous and uniform film. Since silver particles in the form of islands have the localized surface plasmon absorption in the visible light region, the transmittance of the silver thin film is disadvantageously decreased.
When an underlayer composed of a metal other than silver is formed under a silver thin film to have a thickness smaller than that thereof, a continuous and uniform silver thin film is obtained instead of being placed into an island state; hence, as one of measures for the above problem, a technique has been proposed in which a transparent conductive laminate film having an excellent transmission property as compared to that of a thin film of a silver element is formed (see Japanese Patent Laid-Open No. 2008-171637).